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Proper Usage of DOF Calculator and Hyperfocal values (1 image)
Hello,.

I recently started using the CHDK firmware for the G7. I'm very happy with it thus far and it definitely extends the capability of my camera..

2 of the 'features' included in the CHDK are a DOF calculator and a misc. values calculator (includes focal length, focus distance and aperture value)..

On the CHDK wiki, it gives instructions of a sort for using these values to obtain good DOF and Hyperfocus, via R1, R2 and focus distance but I find them vague. I.E., I understand what R1 and R2 are, and that the difference between the two is your DOF, but I'm a bit confused about the last sentence, which instructs to 'set the focus point (F on the misc. value scale) to the hyperfocal distance to obtain (see Using DOFCalc.jpg)..

The only way I can see to accomplish this is to use manual focus? But setting MF to the HYP seems to create a blurrier image..

The images below show what I've just detailed above, including the instructions. I am hoping that someone here will be able to explain this more fully, yet simply..

Thanks for any input,abana.

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Comments (9)

Have you taken any actual pictures with your setting?.

While composing your image, the camera keeps the aperture WIDE open until the moment you press the shutter. Then it stops down the aperture and takes the actual pictureWarm regards,DOF..

Comment #1

Dad_of_four wrote:.

Have you taken any actual pictures with your setting?While composing your image, the camera keeps the aperture WIDE openuntil the moment you press the shutter. Then it stops down theaperture and takes the actual picture.

Hi DOF. Thanks for responding. I'm not sure which setting you mean...the one in the image or where I've adjusted the focus manually to match HYP?.

Of course, the settings in the image were just from a half shutter press while the G7 was sitting on my desk for the sake of illustration, and the mode was AV, flash on. I have taken a few shots using MF to match HYP, but they diodn't come out that great (this was in my office...the weather here has been bad), i.e, they were poorly focused. This is why I'm hoping for an explanation for using these values to determine & insure image sharpness via the calculator and misc. values. It would surely be useful!.

I mostly use center weighted Flexizone, but have noticed that the F & HYP values are much closer using AiAF. Nonetheless, there are times when Flexizone is needed, especially when using AEB for HDR purposes..

Thanks again,abana..

Comment #2

Abana wrote:.

The only way I can see to accomplish this is to use manual focus? Butsetting MF to the HYP seems to create a blurrier image..

Your focus distance is about 0.5 (meters?)..

Hyperfocal distance at the selected aperture and focal length is 1.92 meters. If you set the focus distance to 1.92 meter, then everything from 0.96 meters (i.e. half hyperfocal distance) to infinity should be acceptably sharp..

Your subject is at about 0.5 meters, so it will not be sharp..

Seen in a fortune cookie:Fear is the darkroom where negatives are developed..

Comment #3

Abana wrote:.

I recently started using the CHDK firmware for the G7. I'm very happywith it thus far and it definitely extends the capability of mycamera..

I don't know anything at all about the G7, I just happened along, so my comments are generalised..

On the CHDK wiki, it gives instructions of a sort for using thesevalues to obtain good DOF and Hyperfocus, via R1, R2 and focusdistance but I find them vague. I.E., I understand what R1 and R2are, and that the difference between the two is your DOF, but I'm abit confused about the last sentence, which instructs to 'set thefocus point (F on the misc. value scale) to the hyperfocal distanceto obtain (see Using DOFCalc.jpg)..

Looking at the screen shot, the numbers just didn't initially make sense until I started typing a reply and checked some numbers. It appears to tell you that your closest point of acceptable sharpness (R1?) is 0.38 - the furthest point (R2) is 0.63 and the DOF is 0.25 - correct, the difference between R1 and R2..

But then it gives a Hyperfocal distance of 1.92 - if you focus at 1.92 (metres I've assumed) your points of focus won't be within a meter - they'll be from just under a meter away to infinity (i.e. R1 would be 0.96 and R2 would be infinity) - that's how hyperfocal works - the hyperfocal distance is a point in front of you, determined by the focal length and aperture of the lens, where if you focussed, everything from half way to that point and then to infinity would be within acceptable sharpness. Or conversely and more correctly, if you focussed at infinity, everything from infinity to half of the hyperfocal distance would be within acceptable sharpness..

The numbers on the display for R1 and R2 relate to the focus distance actually chosen - 0.47 - so focusing at 0.47m would give you the DOF and near and far points of acceptable sharpness indicated at the top left - checked and corroborated at http://www.dofmaster.com/dofjs.html In this instance, hyperfocal distance is not pertinent as you're wanting to focus closer than it becomes relevant..

The hyperfocal distance indicated is where you'd need to focus to get infinite DOF. If you change F to 1.92, you'll get the same hyperfocal, as that is determined by aperture (f4.75) and focal length (7.4mm) but now R1 would become 0.96 and R2 would be infinity..

Hyperfocal is perhaps more relevant when taking landscapes and the like, I use it all the time for that type of shot, but perhaps less worthwhile for closer subjects like the scene you appear to have been focusing on - in which case, I'd recommend ignoring the hyperfocal figure and just work with your desired focus point within the scene and using the R1, R2 and DOF figures to determine if you need to change aperture to get the DOF you desire for that scene..

The only way I can see to accomplish this is to use manual focus? Butsetting MF to the HYP seems to create a blurrier image..

It will in that particular scene, as described above, as you're actually focusing further away than the scene needs - if you took the shot at the hyperfocal distance, everything closer than a meter would be out of focus. Try the same thing on an outdoor scene with distant objects and you'll find it much more useful. For close scenes, the R1, R2, DOF and F figures are more relevant..

So many photos, so little time.http://www.peekaboo.me.uk - general portfolio & tutorialshttp://www.boo-photos.co.uk - live music portfoliohttp://imageevent.com/boophotos/ - most recent images.

Please do not amend and re-post my images unless specifically requested or given permission to do so...

Comment #4

I've never seen any of this stuff before but I can see right away why you are confused..

There is no connection between R1/R2 and HYP. They relate to different ways of focusing the camera:.

1) With the current settings, i.e. focal length 7.4mm, aperture f/4.75, focus distance 0.47m - the depth of field is from 0.38m to 0.63m..

2) A completely separate calculation - with the current focal length 7.4mm and aperture f/4.75, the hyperfocal distance is 1.92m. As the instructions say, the camera will be in focus from "some near distance" to infinity - but it doesn't tell you what distance that is. However using http://www.dofmaster.com/dofjs.html it turns out to be 0.96m, so yes, your subject at 0.47m will be well out of focus. (Oh, and yes, you do have to set the focusing distance to the hyperfocal distance manually.).

The idea behind using R1/R2 is to ensure that you have the depth of field you need, without having more than you need..

The idea behind using hyperfocal distance is to get the maximum possible depth of field, at the focal length and aperture you are using..

HTH...

Comment #5

Thanks for all of the very helpful & informative responses! After I last posted tp this thread, I did some more research, and between the posts here and this link ( http://www.dofmaster.com/hyperfocal.html ), I think I have a much better understanding of what all the scales mean and how I can apply them..

In fact, I took some shots today using the scales as explained here and achieved some very sharp images, front to back. My images are generally landscapes or scenics with depth. That's what I enjoy, but many of my images seemed to have some areas that just weren't sharp through and through. I couldn't figure out why, but this seems to be the solution!.

So now I understand Hyperfocal distance, have a better understanding of DOF and have new tools to acheive what I want with my images..

And if I understand correctly, I ignore HYP for the closer images and just monitor DOF and focus distance. If I am in error here, please correct me..

And again, thanks to all who have responded here. Your help has been invaluable and is what has made this forum a great place to learn..

Abana..

Comment #6

Abana wrote:.

In fact, I took some shots today using the scales as explained hereand achieved some very sharp images, front to back. My images aregenerally landscapes or scenics with depth. That's what I enjoy, butmany of my images seemed to have some areas that just weren't sharpthrough and through. I couldn't figure out why, but this seems to bethe solution!.

The hyperfocal technique is ideal for landscapes, probably less so for other and closer subjects. It seems to be a very common newbie misconception to think that for a significant DOF in landscapes, you need to stop the aperture right down (I often see landscape EXIF posted with f16 and f22 apertures) - when in fact, using the lens sweet spot and careful focusing is more successful. My landscapes improved significantly when I started thinking in that way - with my DSLR I take all my landscapes and panos between f8 and f11 and with compacts, usually around f5..

So now I understand Hyperfocal distance, have a better understandingof DOF and have new tools to acheive what I want with my images..

Use them as a supplement to your own understanding - don't just slavishly use the figures, use them as a tool to corroborate what you already think is the way to take something..

And if I understand correctly, I ignore HYP for the closer images andjust monitor DOF and focus distance. If I am in error here, pleasecorrect me..

I just juggled some figures and as far as I can quickly ascertain, for practical purposes, for the G7, at the widest angle and mid-range aperture, HYP doesn't get much closer than 2m (it does if you stop down ridiculously beyond what I'd recommend you'd even use) and of course using HYP focusing would give you almost infinite DOF - which if there's nothing more that 6 feet from you, isn't actually needed..

So my advice would be - for closer subjects - to set an aperture you think you need/want, focus where you think you'd like the scene focused, *then* look at R1, R2 and the DOF - just to ensure you have sufficient DOF - if you don't, you can stop down, zoom back out, or step further away - or a little of each, until you get the DOF you'd like. ***.

For outdoor scenes, repeat the framing and setting up process and then look at your screen and see where HYP is. Use that number in conjunction with the others, so see what sort of DOF and R1 you get - if for example, it gives you the HYP of 1.92 in your example and you focused at that point, it would now give you an R1 number of 0.92m - if the closest object is 5m from you, you don't necessarily need to actually focus that close, there are some schools of thought that say that focusing a bit further away than the HYP gives you more detail at infinity. It's something I now do if I don't actually have close details. If you have a front-most focal point in your scene further away than HYP and it's the subject of your photo - just aim to ensure that is in focus..

Use the numbers as a tool to supplement your own thinking, don't use them to substitute it. It's only the same as the generalised rules I keep in my head, which inform my decisions on aperture and where to focus, but there are many things to consider when setting up a shot and this is just another tool in your arsenal..

*** I have a tutorial on DOF etc. which might be helpful - it's written about DSLRs, but the information is still valid for all cameras, even if the numbers aren't. See: http://www.zenadsl5251.zen.co.uk/photos/doftut.html.

So many photos, so little time.http://www.peekaboo.me.uk - general portfolio & tutorialshttp://www.boo-photos.co.uk - live music portfoliohttp://imageevent.com/boophotos/ - most recent images.

Please do not amend and re-post my images unless specifically requested or given permission to do so...

Comment #7

Boo wrote:.

Focusing a bit further away than the HYP gives you more detailat infinity..

Sure does..

DOF is the range where the image is acceptably sharp, at a certain enlargement. But there is only one infinitely thin plane of sharpest focus. The image is blurrier the further you get from this plane, until it gets unacceptably sharp..

If hyperfocal focusing was sufficient, telescopes wouldn't have focusing mechanisms..

Also, what is acceptably sharp? The "standard" Circle of Confusion (CoC) on which most DOF calculations are based assume somebody with normal vision viewing an 8x10 at 10 inches. But there is no correct CoC. Use what works best for your intended purpose. CoC is different if you assume 4x6 or wallet size at the same distance, a poster at 10 feet, a Billboard at 500 feet, or 100% pixels on your monitor 15 inches away..

Seen in a fortune cookie:Fear is the darkroom where negatives are developed..

Comment #8

All Very good advice. Thank you for taking the time to post it. And thanks for the link to your site. Lots of info and very nicely laid out (and easy on the eyes!). I've read some of the material there and have bookmarked for later return..

Thanks again to all for contributing to my education,abana..

Comment #9

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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